Artificial limb



Aug. 9, 1949.

6 Shets-Sheet 1 Filed Aug. 10,. 1946 m mw M E mm a 2 0 6 O 8 6 5 6 4 H x u a m l n E I. H. 4 8 F v. 6 6 4 I B O 8 8 4 8 II. My. 3 M w M Hm 8 I M 2 4 6 H l m 6 O 0 k1 mQ IFJFFF 6 5 w 6 \4 a I... Q ul v i llllllll 0 s 2 Q 2 F m 4 2 3 ATTORNEY.

Aug. 49'- J. H. F. STEWART 2,478,721

ARTIFICIAL LIMB Filed Aug. 10, 1946 6 Sheets-Sheet 2 F7 5' 1U 1U FIE 5 INVENTOR. JOHN H .F. STEWART.

ATTORNEY Aug. 9,1949. J. H. F. STEWART ARTIFICIAL LIMB Filed Aug. 10, 1946" 6 Sheets-Sheet 4 FIE EU INVENTOR. JOH N H, F. STEWART.

ATTO PNEY.

Aug. 9, 1949. J. H. F. STEWART ARTIFICIAL LIMB Filed Aug. 10, 1946 6 Shets-Sheet 5 moi AWN mrnh m m k QWN mbhw T. m R mm. m m H N H O J \ONN omw v: m 3 wm I? GE ATTORNEY.

Aug. 9, 1949. J. H. F. STEWART ARTIFICIAL LIMB 6 Sheets-Sheet 6 Filed Aug. 10, 1946 im END INVENTOR. JOH N H .F. STEWART.

ATTORNEY amt Aug. 9, 1949 "UNITED STATES PATENT OFFICE John H. F. Stewart, Mount Clemens, Mich.

Application August 10, 1946, Serial No. 689,724

This invention relates to artificial body members and more particularly to an artificial leg.

It is an object of the present invention to provide a novel artificial leg construction with selfanlmation of both knee and ankle joints in a manner which closely simulates the animation of a natural leg.

In its preferred form, the present invention embodies 'nydraulic means associated with the knee and with the ankle joints and so interconnected and controlled as to coordinate the bending of the ankle with the bending of the knee at proper times during normal walking. ,At the same time, the same hydraulic elements are preferably utilized to supervise each other in such a way as to add greatly to the safety of the prosthesis under abnormal or diificult walking conditions.

It is an object of the present invention, therefore, to provide a device of this character with improved hydraulic actuation and control means for the joints which enables a user to walk naturally, with greater safety and which will, furthermore, be capable of use for running, dancing and other activities where prior prostheses cannot be readily used, including even the use by double amputees without canes or crutches.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein apreferred form of the presentinvention is clearly shown.

In the drawings:

Figure 1 is a side view of an artificialleg incorporating a preferred form of the present invention.

Figure 2 is a fragmentary rear view of the leg shown in Figure 1.

Figure 3 is a top view of the bottom portion of the thigh socket.

Figure. 4 is a rear view of the hydraulic actuation and control unit.

Figure 5 is a side viewof the unit of Figure 4.

Figure 6 is a vertical sectional view on line 6-6 of Figure 4.

Figure '7 is a vertical cross section on line 'l-| of Figures 4 and 10.

Figure 8 is a horizontal cross section on line 8-8 of Figure 6.

Figure 9 is a vertical cross section on line 8-9 of Figures 4 and 10.

Figure 10 is a top view of the unit shown in Figure 4. T

F gure 11 is a fragmentary vertical cross section online l|-ll of Figure 10.

39 Claims.

Figure 21 is a vertical cross section on line 2|2l of Figure 8.

Referring now to Figures 1, 2 and 3, the embodiment there illustrated comprises a pelvic band I!) universally jointed to a thigh member l2. This in turn is pivoted to a shin member M at the knee joint l6, and a foot member I8 is pivoted to the shin by an ankle joint 20. Articulation of the pelvic band ill to the thigh socket I2 is preferably obtained by a semicircular yoke 22 pivoted to the thigh on a fore and aft horizontal axis at and carrying an eye bolt 26 adjustably but rigidly, secured thereto. Another eyebolt 28 is pivotally secured in a boss 30 attached to the band 10 and is pivoted on a horizontal lateral axis at 32 to the eye bolt 26. The yoke 22 is adjustable laterally in and out by means of a frictional clamp 25 and may also be adjusted circumferentially to some extent so as to locate the pivotal axis 32 as closely as possible to the extension of the natural hip pivot.

The thigh member I2 may be formed of any suitable material so as to provide a socket for the amputated stump of the user and is provided with a flat bottom wall 34 having a plurality of elongated holes 36 by which a knee bracket 38 may be secured thereto in an adjustable manner. The knee bracket 38 has two pairs of ears 40 for the reception of the pins forming the pivot at It and receives suitable eyes 42 formed at the upper end of the shin member l4. The latter is preferably formed as a truss-like welded tubular structure comprising a pair of trusses, one at either side, as shown in Figure 2. Similar eyes 44 are formed at the lower end of the shin member to receive the pin at the ankle joint 20. The foot member comprises a welded tubular structure having a toe section 46 resiliently pivoted at its forward end and a rigid heel 48. The structure as a whole may be provided with any suitable rigid or semirigid externalcovering to simulate the shape of the natural leg. The particular configurations of the structural parts shown are intended as illustrative only and it will be understood that so far as the present invention is concerned, the thigh member," "shin member," and foot member referred to hereinafter and in the claims may be of any suitable form to receive and be connected with additional structure to form a completely finished thigh, shin, and foot, respectively.

Pivotally mounted on the shin member I4 at 50 is a hydraulic unit 52. The unit 52 has an upwardly extending knee piston rod 54 which is pivotally connected to the bracket 88 and is preferably biased upwardly by a'spring 58. The pivot point 58 is preferably located as shown in Figure 1 slightly to the rear of he knee pivot I6 and slightly above the same so that as the knee is bent, the entire hydraulic unit 52 is swung counterclockwise on the pivot 50 to permit the knee to be bent considerably beyond 90 degrees from the position shown in Figure 1 without interference between the thigh member I2 and the shin member I4. The hydraulic unit 52 also has a downwardly extending ankle piston rod 80 which is biased downwardly by a spring 52. The rod 60 is connected at 54 to a link 88 which ispivoted at 88 to the foot member I8 somewhat to the rear of the ankle pivot 20. The location of the piston rods 54 and 80 is preferably such that in all positions their center lines intersect the pivot point 50 for the hydraulic unit 52.

Referring now to Figures 4 through 119, the construction of the hydraulic unit 52 is there illustrated, It comprises essentially a doubleacting knee cylinder and piston connected to the rod 54, a double-acting ankle cylinder and piston connected to the rod 50, a transfer cylinder, a pressure fluid reservoir and certain automatic and manual control valves. As shown more clearly in Figure 6,, the knee cylinder 10 is provided with a liner 12 in which a piston 14 connected to rod 54 is slidable. The upper end of cylinder 10 is closed by a cap 15 and an O-ring seal 18. A shaft seal 80 of the type shown in my Patent No. 2,332,763 forms a sliding seal for the rod 54. The piston 14 is also provided with a similar sliding seal 82. Formed in the lower portion of the hydraulic unit is an ankle cylinder 84 provided with a liner 85 and having a sliding piston 88 connected to the rod 50. An end cap 80 closes the lower end of the cylinder and is provided with an O-ring seal 92. The end caps 90 and 18 are provided with sliding bearing extensions 84 and 85, respectively (see Figure 4). Cap 80 is also provided with trunnion arms 91 for pivotally supporting the unit 52.

The piston 88 and rod 50 are provided with a central bore 98 closed at its lower end in which is slidably mounted a control valve sleeve I00. The latter has a stem I02 projecting upwardly through the body of the unit and aspring I04 which biases the valve sleeve I downwardly. The valve sleeve I00 is normally stationary but may be adjusted upwardly and downwardly for a purpose later to be described. It coacts with a plurality of small ports I08 connecting between the bore 98 and the space beneath piston 88. Sliding seals I08, H0 and H2 are provided for the rod I02, piston 88 and the piston rod 50, respectively.

It will thus be seen that the structure thus far described provides aslidable knee piston 14 dividing the cylinder into an upper chamber H4 and a lower chamber II8, while the ankle piston 88 divides the cylinder 84 into an upper chamber I I8 and a lower chamber I20.

Also formed in the body of the unit 52 is a fluid reservoir I22 (see Figure 'I). This is provided with a floating piston I24 having a sliding seal I26 and is biased downwardly by a spring I28. The upper end of the cylinder I22 (see Figure 5) is closed by a cap I retained by a snap ring I32 and having a vent hole I84. The reservoir cylinder I22 connects directly to the upper angle cylinder space I I8 by a drilled passage I28. Another drilled passage I88 extends from the outside of the unit to connect with the space H8 and contains a charging valve I40 similar to an ordinary tire valve and is closed by a screw plug I42. The passage I intersects a horizontal bore I44 which contains an automatic valve comprising a sleeve body I48 stationarily mounted in'the bore I44 and a sliding spool I48. The left-hand end of the spool is exposed to reservoir pressure by a plurality of small passages I50 while the righthand end of the spoolis in communication with a passage I52 closed at its upper end by a plug I54. A short transverse passage I55 (see Figure 4) connects to the upper knee cylinder chamber I I4. The right-hand end of bore I44 is closed by a screw plug I58 which carries a pin I50 having a tapered end adapted to be received in a bore I82 in the spool I48 for the purpose of cushioning the movement thereof. A spring I54 normally biases the valve I48 to the left in Figure 'I.

The sleeve I48 has ports I58 communicating with passage I85 and ports I58 communicating with a passage I10 (see Figure 8). In the normal position of the valve illustrated, these ports are connected but when the valve is shifted to the right, ports I85 are blocked. Passage I10 communicates with a valve bore I14 adapted to receive an adjustable restriction valve I15, later to be described. The valve I15 controls the flow between a passage I18 leading from the lower knee cylinder chamber H5 and passage I10. The passage I10 has an extension I80 connecting with a valve bore I82 which contains a stationary sleeve I84 and a sliding spool I85. The righthand end of bore I 82 Is closed by a screw plug I88 and the spool I88 is biased to the right by a spring I90. The stem I88 of spool I85 slides in a sleeve I81 secured to sleeve I84 and forms a dashpot chamber I89. This serves to retard shifting movements of the spool by the restriction of fluid passing into and out of chamber I89 through the clearance between stem I85 and sleeve I81.

Referring now to Figure 9, the valve bore I 82 communicates by a passage I82 with a transfer cylinder I94. The latter has a floating piston I85 provided with a seal I88 and dividing the cylinder into an upper chamber I85 and a lower chamber I91. A spring I98 urges piston I88 downwardly at all times. closed by a cap 200 retained by a snap ring 202 and having an O-ring seal 204. The cap 200 also has a communication groove 208 which connects with the inner face of the cap by a hole 208 in the cap and connects with the upper knee cylinder space II4 by a hole 2I0 in the body of unit 52. The right end of bore I 82 in Figure 9 communicates with the upper ankle cylinder space II8 by a passage 2I2. The valve spool I85, when in the position illustrated. establishes communication between a set of ports 2 I8 communicating with passage I82 and a second set of ports 2I8 communicating with passage I80 (see Figure 8). when the valve spool is shifted to'the right in Figure 9, the passages 2 are blocked.

The bottom ankle cylinder space I20 is in communication with a vertical passage 220 which intersects the valvebore I 82 at its left-hand end in Figure 9. The passage 220 is closed at its upper The upper end of cylinder I94 isend of the bore.

end by a screw plug 222 and communicates directly with the upper knee cylinder space I14 by a passage 224. Passage 224 enters the knee cylinder at a point below the top thereof so that it is closed 01! by the piston 14' (see Figure 8) before the piston reaches the upp r limit of its stroke. The passage 220 also communicates with the space II4 by means of'a passage 228 (see Figure 12) which intersects a check valve chamher 228 closed by a screw plug 280. A passage 282 jconnects from the chamber 228 to the upper end of space H4 and a ball check valve 284 prevents flow into the space II4 through this path.

Referring again to Figure 9, the body of the unit 52 is provided with a passage 288 having a check valve 238' therein and closed at its outer end by a screw plug 240. The discharge side of the check valve 238 communicates with passage 22 0 by a short horizontal passage 242. 4

Referring now to Figures 1 and 6, there is provided a manual control for the valve sleeve I00 comprising a Bowden .wire cable 248 having an operating wheel 248 secured to the upper portion of the, socket I2. wardly through a bracket 250 formed on the hydraulic unit 52 and connects with the stem 102 for the purpose of raising and lowering the same. The lower end of the stem I02 is not rigidly secured to the valve sleeve I00 but has a head 252 provided with a slot 254 for fluid communication purposes. The head 252 normally rests on a shoulder in the interior of sleeve I00 and the latter is biased downwardly against the head 252 by the spring I04. when the rod 80 and piston 88 are moved upwardly slightly beyond the position shown, the sleeve I00 bottoms at the lower end of bore 98 and is carried upwardly along The cable 246 extends down-.

with the rod 80 compressing spring I04 without further upward movement of the stem I02.

The valve I18 contained in bore I14 comprises a stationary sleeve 255 pressed into the bottom The sleeve 255 is provided with two diametric slots 258 and has a central bore which receives a headed cylindrical piston valve member 258. The valve member is also provided with a diametric slot 260. A light spring 262 urges the valve 258 into the position shown. Rotatably mounted in the outer end of bore I14 is a plug 264 having a seal 288. The plug 284 is retained in the bore by a snap ring 288 and has a square socket 210 slidablybut non-rotatably associated with a square stem 212 formed on the valve 258. The plug 284 also has an outwardly extending operating stem 214 by which the latter may be rotated.

The stem 214 has an operating lever 216 (see Figure 4) provided with a leaf spring 218 urging I the lattercounterclockwise. The end of the lever 216 is connected to a Bowden wire control cable 280 which extends upwardly to a manual control assembly 282. The latter comprises a tube 284 having a, series of perforations 288 at suitable locations and a leaf spring 288 having a handle 290 "is secured to the upper end of the Bowden wire leg in detail, certain considerations relating to the action of walking whether with natural or artificial legs should be considered. For purposes of clarity, a single complete step of one leg may be considered as six separate parts some of which may slightly overlap with each other.v These deceleration.

In the normal walk of an able bodied p rson."

these parts of the step involve the following actions: During foot placement,

downwardly and the heel contacts the ground first. Thereafter, the ankle bends to depress the toe and place the foot in full contact with .the ground. This ankle movement sometimes overlaps with the following part and is also accompanied by a slight knee bend and subsequent straightening. The beginning of foot placement is diagrammed in Figure 14a. During body ascension, the body moves forwardly and upwardly pivoting about the ankle and the knee remains straight. The forward body movement is derived partly from momentum and partly from forward propulsion by the opposite foot. The beginning of body ascension is diagrammed in Figure 15a. When the leg is substantially vertical, body propulsion begins as shown in Figure 16a. This consists primarily of a falling forward with the knee straight but instead of pivoting about the ankle. the ankle is held rigid and the foot rocks up onto the toe portion. During body propulsion, the entire body weight is supported on the leg under consideration.

Foot disengagement, while considered separately-for the present'purposes, actually merges with leg recovery-acceleration. As the body weight is relieved from the leg, the thigh is swung forwardly about the hip. This together with the inertia of the shin and foot and also the frictional drag of the toe on the ground causes the knee to bend. Foot disengagement is shown about to start in Figure 17a. Leg recovery-acceleration.

bringing it to a stop and a rapid inclination of the shin forward, with a resulting straightening of the knee. At the same time the ankle bends to depress the toe somewhat so that the leg is again ready for foot placement. The present invention aims to duplicate to a large extent in the artificial leg these natural actions.

The operation of the device can best be understood from Figures 14 and 14a through 19 and 19a which show the positions of the parts and the fluid flow conditions during these six stages of .a single step. With the device entirely filled with oil starting from the position shown in Figure 14, the leg is in the position indicated in Fgure 14a where the thigh has been swung forward to its maximum extent and the heel has just been placed on the ground. Under these conditions the fiuid reservoir I22 and its spring pressed piston I24 maintain a light pressure, as for example, 50 pounds per square inch; as indicated by the dotted arrows with Kshaped heads which indicate maintenance of pressure without any flow taking place. In this and in the following diagrams solid arrows are used to indicate the flow which takes place diu'ing movement from parts are (1) foot placement, (2) body ascension. (3) body propulsion. (4) foot disengagementflfi) F leg recovery-acceleration, and (8) leg recovery I the knee is straight, the thigh and shin project forward and the position shown in one diagram to that shown in the next.

Valve I86, before the heel touches the ground, is in its open position as shown in Figure 14 due to the higher pressure maintained in chamber I20 as compared with that in reservoir I22. This higher pressure is due to the force of spring 82 plus the increment of pressure obtained by the diiferential area of chambers H8 and'I20 and this pressure holds check valve 238 seated. The first action which takes place between Figures 14 and 15 is the upward movement of the ankle piston 88 caused by the swinging of the foot into position parallel with the ground. This action takes place freely and piston 88 moves upwardly opposed only by the spring 52 and the fluid pressure from reservoir I22 exterted over an area equivalent to the area of rod 60. Oil flows at first from chamber II8 through conduit 238, check valve 238, conduits 242 and 220, to the chamber I20. After a slight upward movement, flow can take place additionally through the apertures I 06, as shown by the dotted arrow. This flow may be restricted somewhat by ports I06 to prevent slapping of the toe on the ground at this time. At the start of upward movement of piston 88, the valve I86 moves to the left due to equalization of pressures at its opposite ends permitting the spring to force the valve over. A small momentary flow occurs from line I36 through line 2I2 to valve I86 and from there through line 220 to chamber I20. At about this time, the body weight is transferred to the artificial leg and the body swings forwardly pivoting about the ankle joint.

Any tendency for the knee to bend forcing piston I4 downwardly as indicated in Figure 15 will immediately tend to draw a vacuum in chamber II4 since piston I4 is blocking port 224 andcheck valve 234 prevents flow into chamber II4. Accordingly, valve I48 will be pulled over against the spring by the reduction of pressure in passage I52 and by the maintenance of pressure from fluid reservoir I22 in conduits I36 and I50. This looks the knee effectively regardless of the contour of the ground upon which the foot is placed. In other words, the ankle is free to take up any position consistent with the ground contour although the knee cannot bend. It will be noted that at this time the ankle is bent with the toe downwardly thus raising the piston 88 considerably above its normal position.

As the body swings forwardly about the ankle as a pivot, piston 88 moves downwardly toward its normal position causing flow through ports I08. When this position is reached, as shown in Figure 16, ports I06 close. This point is determined by the adjustment of sleeve valve I and for normal walking conditions on level ground will be set to take place when the sole of the foot is perpendicular to the leg axis. When ports I08 close, the spring 62 plus the differential area of the ankle cylinder build up the pressure in chamber I 20 so as to again open valve I88. A very small momentary flow takes place from chamber I20 through line 220 to valve I86, and also from valve I86 through line 2I2 to reservoir I22 thus opening valve I86 against the spring. When ports I08 close. the ankle is locked against further downward movement of piston 88 and the oil in chamber I20 is trapped. It cannot escape through the passage 220 as it is locked at all exits as shown by the dotted K headed arrows in Figure 16. This enables the user to exert forward propulsion by reason of the pivot point transferring from the ankle to the toe, thus giving a greater forward component to the body movement under the action of gravity.

During this time, of course, the opposite leg is being swun forward and at about the time that the heel touches the ground, the leg in consideration is in the position of Figure 17a.

This illustrates the condition at the instant when the weight of the user has been transferred to the opposite leg and is just being released from the leg in consideration. As the weight is relieved from the toe, pressure in chamber I20 and line 220 falls but does not equalize with reservoir pressure due to spring 62 and the dif ferential area. This maintains valve I86 in open position. The thigh now starts to swing forwardly, pivoting about the hip at the beginning of the forward step and due to the frictional contact of the toe with the ground and also due to the inertia of the shin and foot member, this tends to bend the knee forcing rod 54 and piston 14 downwardly. Since there is no possible path for entrance of fluid to the chamber II4, pressure is reduced in this chamber and in the line I52 to a value below reservoir pressure which enables the reservoir pressure acting through conduits I36 and I50'to shift the valve I48 to closed position against spring I84. The fluid discharged from chamber II6 is delivered as shown by the arrows in Figure 17 through conduits I18, I12 and I80, through valve I86 and conduit I92 to the chamber I81 of transfer cylinder I94. Piston I86 is accordingly lifted against its spring and the upper chamber I of the transfer cylinder supplies fluid to the chamber II4 through conduit 2I0. This enables the knee to bend during that portion of the stroke of piston I4 before passage 224 is uncovered. Due to the differential area at piston 14 more oil is pushed out of chamber II6 than is required to fill chamber H4. The excess is permitted to pass to the reservoir I22 by the action of valve I48. This valve automatically regulates -the opening at passage I36 to just the correct size to permit such flow. The action is such as to maintain in chambers H4 and I95 a pressure which is lower than reservoir pressure by an amount equivalent to the force of the spring I64 of valve I48 actin over the end area thereof; and the valve acts analogously to a relief valve to permit the excess fluid represented by the volume of rod 54 to pass into the reservoir I22. The ankle piston 88 remains locked during this movement since fluid cannot escape from chamber I 20 either through ports I06-or line 220.

When the point is reached where piston I4 uncovers passage 224, conditions are as illustrated in Figure 18. As the thigh continues swinging forwardly and the shin begins to follow, the toe would normally dragon the ground unless the hip was bodily raised or the knee excessively bent. To prevent the necessity of this action which creates a limp, the toe is raised in the following manner: The opening of port 224 permits oil to flow from chamber I20 through line 220 into chamber II4 thus equalizing the pressure therein. Consequently, valve I48 is immediately opened by flow from chamber II4 through line I52 to valve I48 from which flow returns through lines I50 and I36 to chamber II8. As the knee continues bending with valve I48 thus opened, piston 14 forces oil out of chamber II6 through the valve I48 to the chamber II8. This forces piston 88 downwardly raising the toe and the oil discharged from chamber I20 is free to pass through the passage 220 and port 228 to the chamber II8. Thus at this time, the knee piston and ankle piston are in a closed circuit and one can transfer oil'to the other. At the same time, the oil displaced previously into the transfer cylinder chamber I81 is enabled to escape through passages I82, valve I88, lines I88 and I18. valve I88 and line I88 to the chamber I I8. From chamber I additional flow occurs through line 228, passages 228 and 2I8 to chamber I88. During all of this action from the moment port 228 was opened, the spring 82 and the reservoir pressure acting over the diflerential area of the piston also exert forces urging the piston 88 downwardly. 1 I

It will be notedthat during this forward movement of the thigh and shin, the toe is raised considerably above normal position as shown in Figure 19a. At this point the knee beginsto straighten and piston 18 accordingly starts mov- .lower end. This in efl'ect maintains the sole of the foot substantially. parallel to the ground during the first movement and during-the latter movement the toe lowers relative to the shin until it comes tozthe position illustrated in Figing upwardly. Since the knee and ankle pistons, 1

ure 14a where another cycle is resumed. The

opening of ports I88 by the piston 88 as it reaches normal position prevents further lowering of the toe as the knee completes its straightening.

During the action thus described, the valve I18 was maintained in the position wherein the slots 260 line up with the slots 288 so that the valve is open to free flow in either direction. The valve may be adjusted as desired to impose progressively greater restriction to bending of the knee as oil is forced out of chamber II8. In'this way thevalve may serve as a means for-regulating the speed of bending of the knee during normal-walking and the operation of the leg may be tailored to suit any individual gait. Re-- gardless of the degree of restriction imposed-the valve 288 alwayspermits free flow into the cham to straighten" be'r H8 and thus enables the knee freely under all circumstances.

. The valve I16may also be used for the purpose of descending stairs in a natural manner. For

,this purpose, the control lever 288 is adjusted With the" stud 282 in the next to the top notch 288 which creates a fairly highdegree of restriction at the valve I18.

. To descend stairs, the leg in consideration is 10- action at I18. At the sametime the ankle is also straightened due to flowas illustrated in Figure 19. In this way, a natural descent of stairs can be obtained wherein each leg lands on alternate steps. I

It will be noted that a valuable feature of the present invention resides in the fact that the reservoir I22 maintains all of the chambers filled with oil and replenishes any leakage which may occur from one chamber-to another automatically at each step just prior to the beginning to the sequence as previously described. This action is shown clearly in Figure 14 and the check valve 288 performs an important function in this respect. The chamber. I28 which is subjected to' the heaviest pressure of any chamber during walking, et cetera, is replenished automatically through check valve 288 from reservoir I 22 at Y the instant the heelis placed on theground. This permits free and rapid'fllling of chamber I 28 as the heel isplaced on the ground in the event that any fluid was lost therefrom during a previous step. It also maintains the charge in chambers II 8 and I88 duringthe conditions indicated in Figure 18.

In order to'obtain the best walking action with the device disclosed, certain relationships should exist-between the various springs illustrated, having. regard for the piston areaov'er' which such springs are effective. It is preferred to make the ports I88 are closed even though'theweight of the user is not placed on theitoe. This creates an action wherein the knee is. normally unlocked duringthe stages shown in Figures 16 through 19, inclusive. aswell as at all times when the leg is freely suspended oi! the As an alterin the'sta'ges illustrated in 16 and 17 only,

first placed on a step beneath. the opposite leg and asthe bodyflweight is swungforward, the

knee bendsas soon as the weight of'the body is 6 transferred to the toe. This shifts valve 188 as shown in Figure 16 and permits the knee to bend and start causing flow as shown in Figure 1'7.

' bends causing flow to'occur as shown in Figure 18. During this movement, of course, the op'posite leg is swung outwardly to land on the step below the one where the leg in consideration is "standing, after which the leg in consideration may be swung outwardly straightening the knee wh h a w ys occurs freely due to the check valve 76 The spring I: is of Principal importanceduring The downward movement of piston 18 is re- 1 the heel.

nate construction, the spring I88 may-be made 1 heavier so that it can only be overcomeibythe additional pressure created in chamber I28 bythe weight of the user being: placed on the toes and as soon as the foot is lifted=from the ground,

as shown in Figure 18, the valve "I88 again closes. With this alternate construction "'an additional passage 288 having a checkTval've' 288. as shown 1 55 in Figure 18 is Permit oil to discharge.

from chamber!" to line I88. passage and Z checkQvalve' m'ay-belocated as indicated by dotted linesin Figure '8. This alternate construction is advantageous inthe caseo'fprostheses for double.

. amputees since .it maintains ptheknee locked at all times except'when the weight of theuser is g on the toes.. The'normal' construction,- on the other hand, maintains the knee unlocked at all times except .when the weight. ofthe user is' on The spring I88jfor valve I88 may'be'relatively light in all cases so that it may be overcome by the pressure from reservoirgl22 whenever there is a slight reduction in pressure in' chamber Ill.

The value of ankle spring 82 is. not critical but it has been found thatsome spring force at this point is of material assistance. It should not,

however, be so heavy asto prevent 're'ady depression'of the toe as shown'in Figures 14 and 15.

it is important that a rapid downward movement of piston 88 be obtained so that the toe will lift quickly to avoid scraping on the ground or tripping on a'curb stone. The spring. is of assistanceand in addition'the spring I89 further speeds this movement by rapidly drivingthe liquid out of chamber I91 and into-chamber H8.

The knee spring 56 is likewise uncritical and, in'fact, may, be omitted entirely in many instances. natural gaits of different users, some requiring assistance in straightening the knee durin the latter part of the forward swing of the thigh.

Another important feature of the present invention resides in the factthat automatic kneelocking can take place only during the initial bending 'of the knee, that is, during the travel of piston "I4 from its upper limit down to the point shown in Figure 18 where port 224 is opened. At any degree-of knee bend beyond this, the knee is free to flex and at the same time the knee and ankle are connected for coordination of motion. It is, of course, possible to-lock the knee at any position by pulling out the control handle 29!) to its extreme position. This, hQW-'. ever, is merely for the'purpose of creating a-rigid leg whenever-such is desired due to unusual circumstances. At'all other times 'whenthe manual lock control 280; is not in looking position, the knee is free tobend' to any degree after it has bent through the first limited movement. This is of great assistance in such cases as sitting,

down and getting up, as well as during the normal walking cycle.

The manualadjustment of valve sleeve loll is particularly useful for such requirements as different heights of various shoe heels and for walking uphill or downhill. It serves to adjust the normal, at rest, position of the foot to make it perpendicular to the legaxis or to raise or lower the foot to any desired degree away from perpendicular.

The entire leg is preferably designedfor minimum weight consistent with necessary strength and for this purpose the body of the hydraulic unit and other large parts are formed of light weight material such as magnesium. In addition the hydraulic cylinders are made with relatively small areas so that maximum pressures of the order of 3,000 pounds per square inch are developed. By careful design in this regard it has been possible to construct a satisfactory leg having a weight of only 5% pounds suitable for a 180 pound user.

It will thus be seen that the present invention provides a greatly improved artificial leg which is entirely self-contained and self-activated to create a very close simulation of the natural walking step. At thesame time, the leg is extremely safe and it is impossible to collapse the same due to walking on uneven ground due to the fact that the knee remains locked whenever any part of the weight of the user rests on the heel.

In distinctionto previous artificial legs, the present leg provides a free swinging ankle at the time of foot placement and requires no limitation on the amount of toe depression which may occur at this time due to uneven ground contour. It is particularly important when the heel rests on a pebble or other obstruction higher than the front part of the foot to permit'sucha'dditional toe depression at this time. The present invention thus assures that there is no tendency for Its chief value. isin fitting-various 12 a v the knee to be bentwhen the body weight comes on to the leg. In other words, apebble under the heel cannot because of limited ankle motion throw the upper part of the shin and thev knee 5 forward to thus bend the kneeand cause it to collapse when weight is placed on it.

Another important feature regarding the pres- ,ent ankle action resides in its ability to lock against toe elevation during the body propulsion part of the step. This permits the leg. to

rock up onthe fore part of the foot for pro-.

pulsion purposes. .Atthe same time. however,

the ankle is not permanently blocked against toe elevation beyond this point. Thus during leg recovcry, the ankieispositively operated by means 7 to lift the toe clear-of the ground and to elevate the same above the lock position which occurs during body propulsion.

. It will also be noted that at the end of leg recovery-deceleration, there is provided a cushioning action to prevent slamming" of the shin 'into fully straight position. This comes about by reason of the closure of port 224 by piston ll 5 and the necessity of forcing further oil out of chamber 1 I 4 through the check valve 2 which imposes significant resistance as compared with the free passage 224.

This same portion of the mechanism performs no a further function during leg recovery-acceleration. During; this part of the step it is necessary with-the artificial legto cause knee bending without muscular assistance at the knee and relying solely on thigh movement from the hip.

5 The present invention assures knee bending by delaying ankle movement until the knee piston 14 has moved downwardly past the port 224. This permits the toe to remain on the ground in frictional contact thus making it easier to bend the knee and not having to rely solely on the inertia. of the shin and foot for thispurpose. Another advantage of the present invention resides in the action of the leg when idle, that is, when the user is standing still and merely casually takes a slight step forward with it. If the users weight is not resting on the artificial leg but it is hanging idly or resting lightly on the ground, the anklespring 62 maintains pressure in chamber I which holds the lock valve Ill open. Thus the transfer cylinder "1 is in direct communication with the knee cylinder H8. Any casual bending of the knee which occurs is resisted by the spring bias on transfer piston I" and as soon as the foot is lifted clear of the ground, the knee has an automatic tendency to straighten. The bias produced in this way may be quite strong so that for any casual standing around and subsequent lifting of the artificial leg, it has a strong tendency to straighten quickly. so A permanent bias on the knee of this nature, however, would be objectionable during normal walking because it would resist bending of the knee during leg recovery-acceleration and would hasten straightening of it during leg recovery- 66 deceleration. By the present invention, the knee bias is removed at such times for the reason that the fluid in chamber I91 is discharged into the ankle cylinder H8 for the purpose of elevating the toe. The opening of valve 8 at this time 70 permits such action to occur.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

,of the knee cylinder and the transfer cylinder What is claimed is as follows:

1. A prosthesis. for amputation at the thigh" comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, a first hydraulic piston and cylinder connected between the thigh and shin members, a second hydraulic piston and cylinder connected between the shin and foot members, and fluid passage means connecting said cylinders for conjoint actuation and control of bending of the knee and ankle joints.

2. An artificial leg comprising a thigh member, a'shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit cooperating with both joints and comprising an expansible chamber mechanically connected between the thigh and shin members to control flexing of the knee, a second expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle joint, and hydraulic conduit means connecting said chambers for the transfer of fluid to and fro between them.

3. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, means constituting a hydraulic chamber expansible and contractible with bending movements of the knee, valve means connected with the chamber for hydraulically looking the chamber to prevent bending of the knee, and means for actuating the valve means in response to force applied to the foot member through-the heel, said valve means unlocking the chamber in response to release of said force.

' in said circuit to lock the chamber against bending of the knee upon application of a force to the foot member through the heel, said valve means being responsive to the release of said force for releasing the chamber.

5. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, means constituting a first hydraulic chamber expansible and contractible with bending movements of the knee, valve means connected with the first chamber for locking the a chamber against bending of the knee, means constituting a second hydraulic chamber expansible and contractible with bending movements of the ankle, and fluid conduit means connected with the valve means to actuate the valve means to knee lockin position upon a reduction in pressure in the last mentioned chamber.

6. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, 2. foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit comprising an expansible chamber mechanically connected between the thigh and shin members to control flexing-of the knee, means normally biasing the knee into straight position when the leg is idle, and means for disabling the biasing means 'during at least thelatter part of the leg-recovery part of a normal step.

7. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, means constituting a hydraulic chamber expansible and contractible with bendin movements of the knee, valve means connected with the chamber for hydraulically looking the chamber to prevent bending of the knee, means for actuating the valve means in response to force applied to the foot member through the heel, said valve means unlocking the chamber in response to release of said force, and a second valve means in series with the first valve means and manually shiftable to impose a predetermined degree of restriction to liquid passing through the first valve means to control the rate of knee bending.

8. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit comprising an expansible hydraulic chamber mechanically connected between the shin and foot members to control flexing of the ankle, and means for locking said chamber in response to a predetermined degree of construction thereof to prevent movement of the foot upward beyond a predetermined position.

9. An artificial leg having thigh, shin and foot members articulated by knee and ankle joints, the ankle joint having an angular range of movement approximately equal to that of an average human ankle, and a hydraulically operatedexpansible chamber device connected to operate and control the ankle, said chamber having means normally preventing elevation of the forepart of the foot beyond a predetermined position where the foot is substantially perpendicular to the shin whereby the ankle is effectively locked during the body propulsion part of a step, said chamber permitting free movement of the foot to any position below said predetermined position when the foot is placed on the ground at the end of the leg recovery part of a step.

10. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a footmember pivoted together to simulate knee and ankle joints, means constituting a doubleacting hydraulic chamber expansible and contractible with bending movements of the knee, means constitutin a second double-acting hydraulic chamber expansible and contractible with bending movements of the ankle, passage means connecting said chambers to pass fluid from the first chamber to the second to cause the forward end of the foot to lift clear of the ground during a forward swing of the thigh while bending the knee and efiective upon straightening the knee during the latter part of the forward swing to lower the forward end of the foot to a predetermined position relative to the shin, and means for varying said predetermined position.

11. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, means constituting a doubleacting hydraulic chamber expansible and con tractible with bendin movements of the knee, means constituting a second double-acting hydraulic chamber expansible and contractible with bending movements of the ankle, passage means connecting said chambers to pass fluid from the first chamber to the second to cause the forward end of the foot to lift clear of the ground during a forward swing of the thigh while bending the knee and effective upon straightening the knee during the latter part of the forward swing to lower the forward end of the foot to a predetermined position relative to the shin, and means including a manually adjustable valve associated with the second chamber for varying said predetermined position.

12. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, means constituting a doubleacting hydraulic chamber expansible and contractible with bending movements of the knee, means constituting a second double-acting hydraulic chamber expansible and contractible with bending movements of the ankle, passage means connecting said chambers to pass fluid from the first chamber to the second to cause the forward end of the foot to lift clear of the ground during a forward swing of the thigh while bending the knee and efiective upon straightening the knee during the latter part of the forward swing to lower the forward end of the foot to a predetermined position relative to the shin, means including a manually adjustable valve associated with the second chamber for varying said predetermined position, and a remote control accessible from adjacent the upper part of the thigh for actuating said valve.

13. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit comprising an expansible hydraulic chamber mechanically connected between the shin and foot members to control flexing of the ankle, means for locking said chamber in response to a predetermined degree of contraction thereof to prevent movement of the foot upward beyond a predetermined position, and means including a manually adjusther, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with said joint and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, means forming a bypass for said chamber. said by-pass imposing a predetermined degree of restriction, and means for locking said chamber to prevent movement of the fore part of the foot upward beyond a predetermined point whereby the foot is permitted to move downwardly or upwardly at a controlled rate to all positions below said predetermined point.

17. An artificial leg having thigh, shin and foot members articulated by kneeand ankle joints, the ankle joint having an angular range of movement approximately equal to that of an average human ankle, and being free, when the foot is first placed on the ground at the beginning of a step, to position both heel and toe on ground of irregular contour without causing bending of the knee, hydraulic means between the shin and foot members preventing toe elevation during the bodypropulsion part of a step, and valve means for releasing said hydraulic means to permit elevation of the fore part of the foot during the leg recovery part of a step.

18. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and a foot member pivoted together to simulate knee and ankle joints, means constituting a hydraulic chamber expansible and contractible with bending movements of the knee, means constitutin a second hydraulic chamber expansible and contractible with bending movements of the ankle, and passage means connecting said chambers to pass fluid from the first chamber to the second to cause the forward end of the foot to lift clear of the ground during a forward swing of the thigh.

19. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee Joint, a foot member able valve associated with the chamber for vary- 5 connected to the shin member by an artificial ing said predetermined position.

14. An artificial leg comprising a shin member, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with said joint and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, means forming a bypass for said chamber, and means for locking said chamber to prevent movement of the fore part of the foot upward beyond a predetermined point whereby the foot is free to move downwardly or upwardly to all positions below said predetermined point.

15. An artificial le comprising a shin member, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with said joint and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, means forming a bypass for said chamber, means for locking said chamber to prevent movement of the fore part of the foot upward beyond a predetermined point whereby the foot is free to move downwardly or upwardly to all positions below said predetermined point, and a check valve permitting free movement of the foot downwardly from any position throughout its range of travel.

, 16, An artificial leg comprising a shin memankle joint, a hydraulic control unit cooperating with both joints and comprising an expansible hydraulic chamber mechanically connected between the shin and foot members to control flexing of the ankle, and means responsive to bending of the knee for hydraulically opera ing said chamber to raise the fore part of the foot.

20. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with both joints and comprising an expansible hydraulic chamber mechanically connected between the shin and foot members to control flexing of the ankle, and means for delivering fluid to said chamber in response to bending of the knee for causing the fore part of the foot to raise.

21. An artificial leg having thigh, shin and foot members articulated by knee and ankle joints, the ankle joint having an angular range of movement approximately equal to that of an average human ankle, a hydraulically operated expansible chamber device connected to operate and control the ankle, and fluid control means operated by the normal movement of the leg in walking for operating said chamber to raisethe fore part of the foot during the leg-recovery part of a normal step.

22. An artificial leg comprising a thigh mem- 17 ber, a shin member connected to. the thigh member by an artificial knee 'joint, a foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit cooperating with both joints and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, means responsive to bending of the knee for hydraulically operating said chamber to raise the fore part of the foot, said last means including an expansible chamber operated by the knee, 2. transfer chamber connected to receive fluid during the first part of a knee bend, and means controlled thereafter by the knee for delivering fluid both from the knee operated chamber and from the transfer chamber to the ankle control chamber to rapidly raise the foot.

23. An artificial leg comprising a thigh memher, a shin member connected to the thigh member by an artificial knee joint, a, foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating V with both joints and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, and means operated by bending of the knee to deliver fluid to said-expansible chamber to raise the foot and including means for storing and later redelivering a part of such fluid.

24. An artificial leg comprising a thi h memher, a shin member connected to the thigh memher by an artificial knee joint, a foot member. connected tothe shin member by an artificial ankle joint, and a hydraulic control unit. coop- 1 crating with both joints and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, means responsive to bending of the knee for hydraulically operating said chamber to raise the fore part of the foot, said last means includin an expansible chamber operated by the knee, a transfer chamber connected to receive fluid during the first part, of a knee bend, and aresiliently biased movable wall for said transfer chamber whereby the knee is normally biased toward straight position by said movable wall actingon the fluid in the kneeoperated expansible chamber.

25. A prosthesis for amputation at the thigh comprising a thigh member, a shin member and afoot member pivoted together to simulate knee and ankle joints, means constituting a hydraulic chamber expansible and contractible with bending movements of the knee, means constituting a second hydraulic chamber expansible and contractible with bending movements of the ankle, passage means connecting said chambers to pass fluid from the first chamber to the second to cause the forward end of the foot to lift clear of joints, the ankle joint having an angular range of movement approximately equal to that of an =average human ankle, a hydraulically operated expansible chamber device connected to the shin and foot members to operate and control the ankle, a second hydraulically operated expansible chamber device interposed between the thigh and shin members to operate and control the knee ioint, and means including a hydraulic circuit connecting said devices and effective to raise the toe in response to knee bending only beyond a predetermined angle during the leg-recovery part of a normal step. 1

27. An artificial leg having thigh, shin and foot members articulated by knee and ankle joints, the ankle joint having an angular range of movement approximately equal to thatof an average human ankle and being free, when the foot is first placed on the ground at the beginning of a step, to position both heel and toe on ground of irregular contour without causing bending of the knee, means preventing foot' elevation beyond a predetermined position during the body propulsion part of a step, and motor means for positively operating the ankle joint to lift the foot beyond that position during the leg-recovery part of a step.

28. An artificial leg comprising a thigh member, a shin member connected to the thigh memher by an artificial knee joint, 2. foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with both joints and comprising an expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle, means for at times locking the knee in response to conditions in said chamber, and means responsive'to bending of the knee for hydraulically operating said chamber to raise the fore part'of the foot.

29. An artificial leg having thigh, shin and foot members articulated by knee and ankle joints, the ankle joint having an angularrange of movement approximately equal to that of an average human ankle and'being free, when the foot is first placed on the ground at the beginning of a step, to position both heel and toe on ground of irregular contour without causing bending of the knee, hydraulic means-betweenthe shin and foot members preventing toe elevation during the body-propulsion part of a step, valve means for releasing said hydraulic means to permit elevation of the fore part of the foot during the leg recovery part of a step, and means operated by the normal leg movement for operating the ankle joint to cause further toe elevation during the leg recovery part of a step.

30. In an artificial leg having a thigh member, a shin member connected to the thigh member by an artificial knee joint, and a foot member connected to the shin member by an artificial ankle joint, a control unit comprising a hydraulic knee cylinder having a double acting piston effective to displace fluid in said cylinder, a hydraulic ankle cylinder having a double acting piston effective to displace fluid in the ankle cylinder, means forming a circuit connecting said cylinders, a knee-lock valve responsive to pressure conditions at the ankle cylinder for blocking now to lock the knee against bending, an ankle control valve responsive to the position of the ankle for by-passing the ankle piston, and means coni trolled by the knee piston for rendering the cir- 19 cult connecting said cylinders, a knee-lock valve responsive to pressure conditions at the ankle cylinder for blocking flow to lock the knee against bending, an ankle control valve responsive to the position of the ankle for by-passing the ankle piston, means controlled by the knee piston for rendering the circuit efl'ective to deliver fluid between the knee and ankle cylinders to operate their pistons in unison during a forward swing of the foot. and a transfer cylinder eflectlve to delay operation of the ankle piston until the knee piston has moved a predetermined amount. and for thereafter accelerating the ankle piston faster than it would be driven by the knee piston alone.

32. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit comprising an expansible chamber mechanically connected between at least two of the members to control flexing of the joint between them, and a resiliently loaded fluid pressure reservoir forming a fluid charging source for the unit, said unit being removable as a self-contained unit without exposing the hydraulic fluid to atmosphere.

33. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint. a foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit comprising an expansible chamber mechanically connected between atleast two of the members to control flexing of the joint between them, valve means for controlling the fluid propelled to and from the expansible chamber, and a resiliently loaded reservoir forming a fluid chargin source for the chamber and for actuatin the valve means in response to a reduction in pressure in the expansible chamber.

34. An artificial leg comprisin a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with both joints and comprising an expansible chamber mechanically connected between the thigh and shin members to control flexing of the knee, a second expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle joint, hydraulic conduit means connecting the chambers in a circuit, and a resiliently loaded accumulator for maintaining a slight superatmospheric pressure in the circuit, said hydraulic unit being entirely sealed oil from atmospheric communication at all points.

35. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, 9. foot member connected to the shin member by an artificial ankle joint, a hydraulic control unit cooperating with both joints and comprising an expansible chamber mechanically connected between the thigh and-shin members to control flexing of the knee, a second expansible chamber mechanically connected between the shin and foot members to control flexin of the ankle joint, hydraulic conduit means connecting the chambers in a circuit, a resiliently loaded accumulator for maintaining a slight superatmospheric pressure in the circuit, and a check valve opening into communication with at least one of said chambers Ior replenishing fluid lost therefrom.

36. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a hydraulic knee cylinder having a double acting piston effective to displace fluid in said cylinder, a foot member connected to the shin member by an artificial ankle joint, a hydraulic ankle cylinder havin a double acting piston eflective to displace fluid in the ankle cylinder, means forming a circuit connecting said cylinders, a knee-lock valve responsive to pressure conditions at the ankle cylinder for blocking flow to lock the knee against bending, an ankle control valve responsive to the position of the ankle for by-passing the ankle piston, means controlled by the knee piston for rendering the circuit effective to deliver fluid between the knee and ankle cylinders to operate their pistons in unison during a forward swing of the foot. and a fluid reservoir resiliently loaded to maintain the cylinders, valves and circuit filled with fluid and to compensate for variations in total displacement volume at different piston positions.

3'7. An artiflcial'leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit cooperating with both joints and comprising an expansible chamber mechanically connected between the thigh and shin members to control flexing of the knee, a second expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle joint, hydraulic conduit means connecting said chambers for the transfer of fluid to and fro between them, and automatic control valve means effective to lock the knee while the leg is placed with the foot forward and to lock the ankle while the foot is supporting the user and to the rear of vertical position.

38. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a foot member connected to the shin member by an artificial ankle joint, and a hydraulic control unit coopcrating with both joints and comprisin an expansible chamber mechanically connected between the thigh. and shin members to control flexing of the knee, a second expansible chamber mechanically connected between the shin and foot members to control flexing of the ankle joint, hydraulic conduit means connecting said chambers for the transfer of fluid to and fro between them, and automatic control valve means effective to lock the knee while the leg is placed with the foot forward and to lock the ankle while the foot is supporting the user to the rear of vertical position, said valve means acting automatically to connect the first and second chambers for conjoint flexing of the knee and ankle when the leg is swung forwardly free of the ground.

39. An artificial leg comprising a thigh member, a shin member connected to the thigh member by an artificial knee joint, a hydraulic knee cylinder having a double acting piston eflective to displace fluid in said cylinder, a foot member connected to the shin member by an artificial ankle joint, a hydraulic ankle cylinder having a double actin piston effective to displace fluid in the ankle cylinder, means forming a circuit connecting said cylinders, a knee-lock valve responsive to pressure conditions at the ankle cylinder for blocking flow to lock the knee against 21 bending, an ankle control valve responsive to the position of the ankle for by-passing the ankle piston, means controlled by the knee piston for rendering the circuit efiective to deliver fluid between the knee and ankle cylinders to operate 5 their pistons in unison during a forward swing of the foot, and a. transfer cylinder effective to delay operation of the ankle piston until the knee piston has moved a predetermined amount and for thereafter accelerating the ankle piston faster than it would be driven by the knee piston alone.

JOHN H. F. STEWART.

REFERENCES CITED The following references are of record in the tile of this 'patent:'

UNITED STATES PATENTS Number Name Date 1,299,980 Marcinko Apr. 8, 1919 1,312,599

Webb Aug. 12, 1919 Number Number 

